A steering apparatus for a vehicle is an apparatus for arbitrarily changing the direction of travel of a vehicle; for example, as illustrated in FIG. 18, the steering apparatus of an automobile is constructed such that it applies a steering angle to the front wheels by transmitting the rotation of a steering wheel 1 to an input shaft 3 of a steering gear unit 2, and pushing or pulling a pair of left and right tie rods 4 as the input shaft 3 rotates. The steering wheel 1 is supported by and fastened to the rear end section of a steering shaft 5, and with the steering shaft 5 passed in the axial direction through a cylindrical shaped steering column 6, the steering shaft 5 is supported such that it can rotate freely. The front end section of the steering shaft 5 is connected to the rear end section of an intermediate shaft 8 via a universal joint 7, and the front end section of the intermediate shaft 8 is connected to the input shaft 3 via a separate universal joint 9.
In the example in the figure, a tilting mechanism for adjusting the vertical position of the steering wheel 1, a telescoping mechanism for adjusting the forward/backward position and an electric-powered power steering apparatus, which uses an electric motor 10 as an auxiliary power source to make it possible to reduce the force required for operating the steering wheel 1, are integrated together. Of these, in order to construct the telescoping mechanism, the steering column 6 is constructed with an outer column 11 combined with and inner column 12 such that the columns can be extended and contracted freely in a telescopic shape, and the steering shaft 5 is constructed with an outer tube 13 and an inner tube 14 combined together by way of a spline fit or serration fit, such that torque can be freely transmitted, and such that the tube can be extended and contracted freely.
When a vehicle, in which the steering apparatus described above is assembled, is in a collision accident with another vehicle, after the initial collision of colliding with the other vehicle, the body of the driver may hit the steering wheel 1, causing a secondary collision. In order to lessen the impact to the driver's body by this second collision, the steering column 6 is supported by the vehicle body by way of a support capsule 16 and bolt 17 so that it drops when a large force is applied in the forward direction. Construction of this section has been widely known in the past such as disclosed in patent literature 1 to 4. FIG. 19 and FIG. 20 illustrate an example of the construction of a section that supports the steering column 6a with respect to the vehicle body that differs from the construction disclosed in the patent literature 1 to 4, however has been generally known.
In the conventional construction illustrated in FIG. 19 and FIG. 20, in order to achieve a tilting and telescoping mechanism that enable the adjustment of the vertical position and the forward/backward position of the steering wheel 1, the middle section of the steering column 6a is supported by a support bracket 18 via a tilting rod 19, and this support bracket 18 is supported by the vehicle body 15 so that it drops when a large force is applied in the forward direction. The support bracket 18 is formed into one piece by joining and fastening together a top plate 20 and a pair of left and right side plates 21, 21′ through welding or the like, the top plate 20 and the side plates 21, 21′ being obtained by bending a metal plate having sufficient strength and rigidity, such as steel plate, respectively.
The portions on both the left and right end sections of the top plate 20 that protrude further toward the left and right sides than the side plates 21, 21′ function as installation plates 22 for attaching the support bracket 18 to the vehicle body 15 so that the support bracket 18 can drop down during a secondary collision. Cut out sections 23, which are open at the rear edge of the installation plate 22, are provided on each installation plate 22. Support capsules 16 are installed on the inside of each of the cut out sections 23. The support capsules 16 are formed by injection molding using synthetic resin, or by die cast molding using a light alloy. The support capsules 16 are supported by the installation plates 22 by fitting installation grooves 25, which are formed on the left and right side surfaces, with both side sections of the cut out sections 23 on part of the installation plate 22. Small through holes 26a that are formed in both side sections of the cut out sections 23 on part of the installation plates 22 are aligned with small through holes 26b that are formed in the support capsules 16, and the support capsules 16 are installed by injection molding or pressure fitting fastening pins (not illustrated in the figure), which are made of synthetic resin or a light alloy, into these small through holes so that they span the small through holes 26a in the installation plates 22 and the small through holes 26b in the support capsules 16. As a result, the support capsules 16 are supported by the installation plates 22 so that they drop down toward the rear from the installation plates 22 only when a large impact load is applied.
Moreover, in this conventional construction, in order to achieve a tilting and telescoping mechanism, the rear section of the inner column 12a on the front side and the front section of the outer column 11a on the rear side are fitted together in a telescopic shape, and by being able to be displaced in the axial direction, the steering column 6a can be extended or contracted. For the steering shaft 5a as well, the rear section of the inner shaft 14a on the front side and the front section of the outer shaft 13a on the rear side are fitted together so that the are able to displace in the axial direction and transmit torque. Of these, the outer shaft 13a is supported on the inside of the outer column 11a by a bearing such as a deep groove ball bearing that is able to support both radial loads and thrust loads so it can only rotate freely. The steering wheel 1 is supported and fastened to a portion of the rear end section of the outer shaft 13a that protrudes further toward the rear than the opening section on the rear end of the outer column 11a. On the other hand, the front end section of the inner column 12a is supported by the vehicle body so that it can pivot up or down around a horizontal shaft 32 (FIG. 18) that is inserted through the tip end section of a support arm 31 that is fastened to the reduction gear casing 30.
In order to be able to adjust the vertical position and the forward/backward position of the steering wheel 1, the front section of the outer column 11a is held between the side plates 21, 21′ of the support bracket 18. The outer column 11a is made by die cast molding using a light alloy, and a held section 33 is provided on the bottom surface of the front section thereof such that it protrudes downward. A slit section 34 is provided in the center section in the width direction of this held section 33, and is such that the diameter of the front section of the outer column 11a can elastically expand or contract. With the slit section 34 held, a pair of long telescopic holes 35 that are long in the axial direction of the outer column 11a are formed in the both sides of the held section 33 such that they are aligned with each other. Furthermore, long tilt holes 36a, 36b that are long in the vertical direction are formed in the side plates 21, 21′ in a partial arc shape with the horizontal shaft 32 as the center and are such that they are aligned with each other. With the long tilt holes 36a, 36b and the long telescopic holes 35 crossing each other, a tilt rod 1 is inserted through these long holes.
The tilt rod 19 is such that a pair of flat sections that are formed on part of both sides in the width direction of the outer circumferential surface of an outward facing flange shaped rim section 37 that is provided on the base end section (right end in FIG. 20) engages with the edge on the side of the long tilt hole 36a. Therefore, the tilt rod 19 does not rotate around its own center axis, however, it can be freely raised or lowered along the long tilt holes 36a, 36b. Moreover, the outer column 11a can displace in the forward or backward direction with respect to the support bracket 18 on which the tilt rod is placed, within a range in which the tilt rod 19 can displace inside the long telescopic holes 36 on both sides. Between the nut 38 that is fastened to the tip end section (left end section in FIG. 20) of the tilt rod and the outside surface of one of the side plates 21′ (side plate on the left in FIG. 20) there is arranged in order from the nut side a thrust bearing 39, the base end section of an adjustment lever 40, and a cam mechanism 41. Of the pair of cam plate elements 42a, 42b of this cam mechanism 41, with the rotation of the cam plate element 42a that faces the one side plate 21′ being stopped by engaging with the edge on the side of the long tilt hole 36b that is formed in this side plate 21′, the cam plate element 42a can be raised or lowered along this long tilt hole 36b. The other cam plate element 42b is engaged to the base end section of the adjustment lever 40 so that relative displacement with respect to this base end section is prevented, this cam plate element 42b rotates as the adjustment lever 40 pivots, and by engaging with the other cam plate element 42a, the thickness in the axial direction of the cam mechanism 41 is expanded or reduced.
When this kind of steering apparatus is installed in a vehicle body, the support bracket 18 is supported by the vehicle body by bolts or studs that are inserted through holes 43 that are formed in the support capsules 16. When adjusting one or both of the vertical position and forward/backward position of the steering wheel 1, the thickness in the axial direction of the cam mechanism 41 is reduced by pivoting the adjustment lever 40 in a specified direction. As a result, the space between the pair of side plates 21, 21′ of the support bracket 18 expands, and the diameter of the outer column 11a expands. In this state, it is possible to adjust the vertical position of the steering wheel 1 within a range in which the tilt rod 19 can displace along the long tilt holes 36a, 36b. It is also possible to adjust the forward/backward position of the steering wheel 1 within a range in which the tilt rod 19 can displace inside the long telescopic holes 35. After the steering wheel 1 has been moved to a desired location with the thickness of the cam mechanism 41 reduced in the axial direction, the adjustment lever 40 is pivoted and displaced in the opposite direction. As a result, the thickness of the cam mechanism 41 expands in the axial direction, and together with the space between the side plates 21, 21′ being reduced, the diameter of the outer column 11a is reduced, and the steering wheel 1 is held in the adjusted position. A balance spring 44 is provided between the support bracket 18 and the tilt rod 19 and supports the weight of the portion that is raised or lowered with the tilt rod 19, such that, during adjustment of the position of the steering wheel 1, the need for a large force for supporting the steering wheel 1 is eliminated.
During a secondary collision, when a strong force is applied in the forward direction to the steering column 6a from the steering wheel 1, the fastening pins that span the small through holes 26a in the installation plates 22 and the small through holes 26b that are formed in the support capsules 16 are sheared. With the support capsules 16 stopped as is in that position, the installation plates 22 displace forward, and the support capsules 16 drop to the rear from the cut out sections 23. As a result of this, the steering wheel 1 is allowed to displace in the forward direction, which lessens the impact that is applied to the body of the user that collided with the steering wheel 1.
In the case of this conventional construction, in the state after the support capsules 16 have dropped to the rear from the cut out sections 23 due to a secondary collision, the vehicle body 15 no longer supports the steering column 6a. In this state, the position of the steering wheel 1 is not set, and it becomes difficult for the steering wheel 1 to apply an adequate steering angle to the steered wheels. Depending on the extent of the collision accident, there is a possibility that even after the support force for supporting the steering column 6a by the vehicle body 15 is lost, regardless of whether the vehicle can or cannot move on its own, the vehicle may have to be moved out of the way by pushing it to the shoulder of the road. In that case, not being able to adequately steer the vehicle using the steering wheel 1 is not preferable.
In regards to this, patent literature 5 discloses construction in which, by inserting an impact absorbing member that is provided on the steering column side in the front and rear direction thereof between members that are fastened to the vehicle body, dropping of the steering column in the downward direction can be prevented even though the steering wheel is displaced in the forward direction due to a secondary collision. However, in this kind of construction, in the state after a secondary collision, the steering column is suspended by way of the impact absorbing member, so construction is complex, and not only does the height dimension (dimension in the vertical direction) of the steering column increase, but after a secondary collision, it is feasible that the supporting rigidity of the steering column will be considerably less than in the normal state. Also, during a secondary collision, often the body of the driver applies a force to the steering column in a direction that causes the steering column to tilt, however, in such a case, relative displacement between the impact absorbing member and the member fastened to the vehicle body is not performed smoothly, and thus the displacement of the steering column in the forward direction is not performed smoothly and there is a possibility that part of these members will become broken.
Patent literature 6 discloses construction in which, by way of a slider provided on the steering column side and a guide rail provided on the vehicle body side, the steering column is suspended such that it can slide in the axial direction. With this kind of construction as well, it is possible to prevent the steering column from dropping down after a secondary collision. However, the construction disclosed in patent literature 6 is even more complex than the construction disclosed in patent literature 5, and it is feasible that the height dimension of the steering column will increase. Moreover, when a force is applied in a direction causing the steering column to tilt, it is possible that the same problem will occur as in the construction disclosed in patent literature 5.